1. Field of the Invention
The present invention relates to a turbomachine fitted with a system for injecting air into a high pressure compressor.
2. Description of the Related Art
A bypass turbomachine has an upstream air inlet that feeds a primary air stream passing through low and high pressure compression stages and then through a combustion chamber, and a secondary air stream surrounding the compression stages and the combustion chamber and joining the outlet of the primary air stream in order to increase thrust.
The high pressure compressor comprises alternating guide vanes and rotor wheels surrounded by an outer casing.
During operation of the turbomachine, a pumping phenomenon can appear, which phenomenon consists in a sudden reversal of the flow direction through the high pressure compressor. This phenomenon is like an impact and may have disastrous mechanical consequences such as breaking blades or damaging sealing devices in the stream through the high pressure compressor.
Separation of the boundary layer of air from the inside surface of the outer casing of the high pressure compressor can lead to disturbances in the air flow of the primary stream, thereby encouraging pumping of the high pressure compressor.
To avoid the boundary layer separating, and thus to increase the pumping margin, it is known to bleed air from a downstream portion of the high pressure compressor between a guide vane stage and a rotor wheel and to reinject the air upstream from the first rotor wheel at the inlet of the high pressure compressor.
That technique involves using an annular air manifold mounted radially around the outer casing of the high pressure compressor. Nevertheless, the space available around the outer casing is already occupied to a large extent by accessories and equipment of the turbomachine such as fuel and oil pipes, electrical circuits, actuators, . . . . In general, the first guide vane stages are variable-pitch stages, having vanes with pivots passing through the outer casing and connected by cranks to respective control rings mounted around the outer casing and actuated by respective actuators or motors housed in said space. It is therefore difficult if not impossible to place a manifold around the outer casing in order to reinject air upstream from the first rotor wheel.
It is not possible to envisage lengthening the high pressure compressor and placing the manifold between the inlet guide vane stage and the first rotor wheel, since that solution would lead to an unacceptable increase in the length and the weight of the turbomachine.